Feather will be OK (hopefully), but the mag motors draw more current on the heavy than the old ones, just have to hope they are more efficent under load. Suppose we could go for killing the other robot in less than 3 minutes as well. Interestingly priced up some Li-pos at under £800 for 10Ah at 36V with more peak current than our current Ni-cads by far. But wihout an incentive to spend any more on robots its hard to justify the cost.